This invention generally relates to a flexible coupling between pipe segments and, more particularly, to a flexible coupling utilizeable in the exhaust system of an automobile power plant.
The U.S. Pat. Nos. 4,097,071 and 4,188,784, patented June 27, 1978 and Feb. 19, 1980, respectively, disclose a high temperature resistant flexible coupling which comprises a spherically surfaced ring seal supported between a tubular end of a first pipe and a free end spherical surface on a second pipe. The second pipe has a flange, and a pair of bolts are resiliently coupled to the flange on the first pipe so as to urge the spherical lip against a high temperature lubricant surface on the ring seal to define a joint so that it readily accommodates substantial angular offset between the first and second pipes while maintaining a positively sealed surface at the joint.
In particular, in the first mentioned U.S. patent, the flanges connected together by the bolts are rigidly mounted on the first and second pipes by the use of a welding technique, the flange on the second pipe being positioned rearwardly of the free end spherical surface with respect to the direction towards the first pipe.
In the second mentioned U.S. patent, the flange on the second pipe is shown to be integrally formed therewith and positioned so as to surround the free end spherical surface. This flange on the second pipe is coupled to the flange on the first pipe by the bolts through a collar mounted on the first pipe on one side of such flange opposite to the tubular end.
A similar flexible coupling is also disclosed in the Japanese Laid-open Utility Model Publication No. 57-148014, laid open to public inspection on Sept. 17, 1982. In this flexible coupling, the flanges on the first and second pipes are shown to have been rigidly mounted thereon by the use of a welding technique, respectively, and that annular portion of the ring seal which is delimited generally between the flanges and is exposed to the outside is radially inwardly recessed so as to define a circumferentially extending groove for minimizing any possible intrusion of foreign matters, such as water and/or mud, into the joint.
The use of conical coil springs one for each bolt for coupling the flanges on the first and second pipes together in a resiliently yieldable manner relative to each other is disclosed in the first mentioned U.S. patent and the Japanese publication.
The flexible exhaust coupling disclosed in all of these prior art references is satisfactory and effective in that the first and second pipes are permitted a relative jolt about the joint, thereby making the pipes yieldable to vibrations transmitted to the pipe system from the engine in operation and/or through the automobile body running on a rough road, without substantially destroying the sealed relationship between these pipes at the joint. However, it has been found that the ring seal is susceptible to damage when subjected to a thermal history for a substantial period of time. More specifically, in the prior art flexible exhaust couplings, the ring seal is generally made of graphite coated exteriorly with a layer of fluoroplastics. Although the fluoroplastic layer facilitates a smooth relative movement between the ring seal and the mating spherical surface on the free end of the pipe while maintaining a gas sealed relationship therebetween, the fluoroplastics itself has a tendency of being decomposed when heated to about 350.degree. C.
On the other hand, because the ring seal is heated not only by the exhaust gas flowing through the pipe system, but also by a friction heat evolved at the spherical joint, it often happens that the maximum temperature of the ring seal may raise to about 420.degree. C. Once the ring seal is heated to such a temperature, the fluoroplastic layer exfoliates from the body of graphite upon decomposition thereof with both the smooth relative movement and the gas sealed relationship consequently affected adversely. In addition, since the exfolication of the fluoroplastic layer permits the body of graphite, contact metal forming the pipe, a rattling sound will be generated from the flexible coupling as a result of the cumulative effect of vibrations and the direct contact of the graphite body with the pipe, and the flexible coupling may consequently be damaged earlier than its normal lifetime.
The problems described hereinabove may equally occur even when the flexible coupling of the construction described hereinbefore is utilized between the pipe and a catalytic converter.